Extended Forecast Discussion NWS Weather Prediction Center College Park MD 135 PM EDT Fri Nov 05 2021 Valid 12Z Mon Nov 08 2021 - 12Z Fri Nov 12 2021 ...Pattern Overview and Guidance/Predictability Assessment... The medium range period (Monday-Friday) begins with a shortwave/upper low exiting the southeast Coast as a deepened surface low off the East Coast increasingly shifts over the Atlantic Monday/Tuesday. Behind this, a stable and warm upper ridge extends from the southern Plains to the Northeast. Out West, an upper low rotating through the Gulf of Alaska/northeast Pacific will send a couple shortwave/troughs across the Western U.S. propagating eastward with time. The models suggest the second stortwave crossing the West Coast around Tuesday of next week may amplify over the Central U.S. mid week with possible upper/surface low development across the Midwest later next week. The latest suite of guidance continues to illustrate a reasonably similar larger scale pettern evolution, but plenty of uncertainty in the details, timing, and strength of systems. Right off the bat, the GFS is different with the exiting Eastern U.S. trough, showing more defined northern/southern stream separation and a stronger/more south surface low well off the Southeast Coast. The 06z GFS is also problematic farther upstream showing a weaker shortwave crossing the Midwest. Bigger issues/uncertainties arise late period as troughing amplifies over the Central U.S. with some guidance showing closed upper low development by Thursday/Friday next week. Run to run variability suggests models struggle with whether this is a feature at all, but regardless should bring at least a defined low pressure system into the Midwest by late next week. This set of WPC progs used a general model blend of the latest deterministic solutions for days 3-4, increasingly blending more towards the ensemble means later in the period. This helped mitigate some of those less uncertain details and timing issues, especially with the late week troughing into the central U.S. and Midwest. This approach maintains good continuity with the previous WPC forecast as well. ...Pattern Overview and Weather/Hazards Highlights... The low off the East Coast should present only maritime threats, though some modestly gusty winds may still be present along the East Coast on Monday. The first system into the upper Midwest early in the week may bring some scattered showers to parts of the Great Lakes/Midwest Tuesday-Wednesday. Meanwhile, the series of Pacific systems will work inland across the West, with upper troughing set to work over the Northwest into midweek. This will highlight periods of terrain enhanced rainfall from the Pacific Northwest to central California and a heavy snow threat from the Cascades to the Sierra and inland across favored terrain for the north-central Great Basin/Rockies with a cooling frontal passage. Amplified upper troughing into the central U.S. is slated to be sandwiched between upper ridges over the West Coast and East Coast within an overall pattern transition. Cyclogenesis and frontogenesis would act to favor an emerging lead rainfall/convective pattern over the east-central U.S. as theta-e advection increases. Backside cold air flow also suggests potential for late next week snows over the Dakotas/Upper Midwest as moisture feeds back around a developing main low. Please see WPC links below for all the details. Initial upper ridging from the southern Plains to Great Lakes/Northeast should result in modestly above normal highs Monday-Tuesday (lingering longer over the Northeast). Mean troughing over the West most of the week should keep temperatures below normal, with eventually translate downstream towards the central U.S. by Friday as near to maybe above normal temperatures move into the West Coast states. Santorelli/Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml